1. Field of the Invention
The present invention relates generally to the field of interventional radiology. More particularly, it concerns a method and apparatus for reconstruction a flow path within a vascular conduit, and even more particularly, it concerns embolectomy and thrombectomy including treatment of thrombosed hemodialysis access grafts.
2. Description of Related Art
More than 129,000 patients are undergoing hemodialysis in the U.S. (Gray, 1997), and the leading cause for hospital admission is a problem related to life-sustaining access (Feldman, 1993). More than 80% of this patient population have a PTFE graft access which provides an average patency of 20 months after placement (Gray, 1997).
If one considers that the arterial and venous anatomy is typically sufficient to support three upper extremity grafts, a dialysis patient may expect an average 10 years (20 months times six grafts) of permanent access availability from upper extremities (Gray, 1997). Depending on the age when the kidneys fail, between 23 and 51% of patients will live at least 10 additional years after starting dialysis (Mailloux, 1994). If a renal transplant does not become available, many patients will need to resort to peritoneal dialysis or a less preferable hemodialysis access such as a lower extremity graft or a hemodialysis catheter. Some patients may even die because of lack of access. Therefore, efforts to maintain each available permanent hemodialysis access have become a matter of paramount importance.
There are at least three primary interventional radiology methods for percutaneous thrombolysis: urokinase infusion, pulse-spray pharmacomechanical thrombolysis with urokinase, and pure mechanical thrombolysis (Bethard, 1996; Trerotola, 1994; Beathard, 1994; Trerotola, 1997). The pharmacomechanical thrombolysis is often expensive because it may require a min. 350,000 and up to 1,200,000 U urokinase (approximately $100/100,000 U. The pulse-spray heparinized saline technique (Beathard, 1994), however, has proved as effective as the pulse-spray urokinase infusion in terms of long-term patency rates. The only statistically significant difference was that a without-urokinase-group took somewhat less time to complete. Recently, it has been found that the added urokinase reduced the rate of clinically asymptomatic pulmonary embolism (detected nuclear medicine perfusion scan), and the complications were more frequent with heparinized saline method (Kinney et al., 1999).
Several devices have been used to perform mechanical thrombolysis. A rotating nitinol basket-like fragmentation cage (Arrow-Trerotola Percutaneous Trombolytic Device) has been used by crossing 5-F sheaths within a graft and requires only a minute or two to restore flow. In a recent study, fifty-one consecutive patients were treated with the device. In all patients, the device was used to treat also the arterial plug in situ at the arterial anastomosis instead of using a Fogarty catheter to reposition the plug as indicated by the device's product labeling. Immediate technical patency was 100% with 6% arterial immobilization (vs 2% control). Adjunctive therapy with an Fogarty Adherent Clot catheter was needed in two procedures (4%). This modified method was found to be safe and effective when the device was used to eliminate the need for an Fogarty embolectomy catheter. (Modified use of the Arrow-Trerotola, 1999). The device costs cca. $500.
The Amplatz mechanical thrombectomy device (Clot Buster) (Microvena Co., has also been used successfully in dialysis grafts (Uflacker, 1996). This 8-F device consists of a gas-driven, high-speed (150,000 rpm) cam that pulverizes the clot. In a randomized series comparing surgical thrombectomy with the device, 89% success was achieved in the device group and 83% in the surgery group. Thirty-day patency was lower with the device (47%) than with surgery (77%). However, residual thrombus may occur with the device, and it cannot be used to treat the arterial plug. Recently the device has been made available also in a 6-French version. The cost of the disposable catheter is $550 and $900 (6-French/75-cm or 8-French/50-cm and 6-French/120-cm or 8-French/120-cm, respectively). The re-usable foot pedal assembly costs additionally. Because the device is not guidewire compatible, a 6-French ID or 8-French ID delivery sheath or a 8-French OD or 6-French OD guiding catheter should be used.
The Hydrolyser catheter (Cordis) uses the Venturi effect to achieve mechanical thrombolysis. The catheter is driven using a conventional angiographic injector. Although thrombectomy was successful in 15/16 instances, five reclotted within 24 h. Secondary patency was 41% at 6 months (Vorwerk, 1994). One concern with this device, however, is the amount of blood aspirated during the procedure (50-150 mL) which could be problematic for these chronically anemic patients. This device is expected to cost $600.
The Cragg thrombolytic brush consisting of a 6-French brush catheter combines mechanical thrombolysis with urokinase to shorten procedure time and reduce urokinase dose. It is not a purely mechanical thrombolytic approach, but it takes advantage of many principles of mechanical thrombolysis. This 6-F device consists of a nylon brush that rotates at low speed (1,800 rpm.) driven by a single-use detachable motor drive. It is not guidewire compatible. It costs $595. Another similar design is the Castaneda Over-the Wire Brush (MTI) which is more preferred because of its guidewire compatibility. The brush itself is modified and allows for using the system forward and backward. The cost is also $595.
U.S. Pat. No. 4,921,484, incorporated herein by reference, discloses a device that uses a tubular mesh in a mesh balloon catheter device. Although this design has shown some utility, it does not offer guidewire compatibility. Thus, it may be necessary to use an additional device(s) to steer towards a desired place within a vessel.
Among simpler devices, the Fogarty Arterial Embolectomy Catheter (Baxter Scientific Products, McGaw Park, Ill.) ($45) has shown some utility in removing arterial clots. Although original Fogarty catheters were not guidewire compatible, guidewire compatible Fogarty balloons (Baxter) ($72) have recently been made available. Other over-the-wire alternatives include occlusion balloons ($110), and PTA balloons ($160-220) to macerate the clots. The basic technique for recanalization of hemodialysis access graft using these devices often consists of a cross-over catheterization requiring, unfortunately, multiple equipment. Specifically, two introducer sheaths and two balloon catheters are used. For dislodgment of an arterial plug or intragraft stenosis, the Fogarty Adherent Clot Catheter (Baxter) ($195) has been successfully used in some cases (Trerotola, 1995). Another similar alternative is the Fogarty Graft Thrombectomy Catheter (Baxter) ($325), which was designed to remove tough, mature thrombus from synthetic grafts. Except for the over-the wire Fogarty balloon, the other designs have no guidewire compatibility.
Despite many advantages, traditional mechanical thrombolytic devices often exhibit significant drawbacks. Some devices are large (8 F or more) and perform poorly in curved vessels, limiting their use in hemodialysis access. Residual adherent clot is a considerable problem with some of mechanical devices. Many devices do not remove the macerated clot and it may be embolized into the lungs. A great number of the available devices cannot be used over-the-wire.
The long term success rates of these methods are generally comparable to those of surgery which should be reserved for failures of percutaneous thrombolysis. Even successful intervention, however, does not eliminate the precipitating factors which cause intragraft thrombosis to occur. Recurrent thrombosis requires further interventions to be made on a regular basis until the dialysis access can be saved. On average, 0.5 to 0.8 episodes of access site thrombosis occur per patient-year of dialysis (Kumpe, 1997). Stenosis at or near the venous anastomosis is the most common cause of late access thrombosis. The endoluminal narrowing can be identified as the cause in cases up to 90% (Beathard, 1994).
Any problems pointed out in the foregoing are not intended to be exhaustive but rather are among many that tend to impair the effectiveness of previously known techniques. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that previous techniques appearing in the art have not been altogether satisfactory, particularly in providing a rapid, effective, safe, easily performed, and minimally invasive outpatient procedure that will restore function to a thrombosed graft or vessel.